When an Ethernet circuit (or other type of circuit) is activated in a network, there is a need to be able to obtain precise performance measurements to make sure the circuit is fully functional in accordance with the performance specification of the operator. Unidirectional (1-way) and bi-directional (2-way) delay measurements are an essential performance measurement that needs to be obtained as part of the service activation. These measurements are also very useful to measure the performance of the Ethernet circuit while IN SERVICE.
These measurements, though useful, do not take into account the multiple segments that may exist within a network path and give no information to isolate the segment delay within the absolute path. To find such a segment over a multi-segment path requires numerous tests, excessive messaging and time.
There is a need to be able to discover a segment by segment latency along a path when an end-to-end latency measurement is requested and not increase messaging as a by-product of this segment by segment measurement.
An example of a unidirectional (1-way) measurement is illustrated in FIG. 1. When a unidirectional delay measurement is requested between network devices 101 and 102 along a network path 103, a test packet 104 is created and a timestamp 105 is inserted into the packet 104 denoting the time when the first bit of packet 104 is transmitted. When the packet 104 arrives at the network device 102, a second timestamp 106 is taken to denote the time when the last bit of the packet 104 arrives at the device 102. The difference in time between timestamp 105 and timestamp 106 denotes the delay in time to traverse the entire path between devices 101 and 102. All intermediate nodes between the devices are not deemed relevant. It is also to be noted that the clocks between the network devices must be precisely synchronized by one of the many methods known to one skilled in the art.
An example of a bi-directional (2-way) measurement is illustrated in FIG. 2. When a bi-directional delay measurement is requested between network devices 201 and 202 along a network path 203, a test packet 204 is created and a timestamp 205 is inserted into the packet 204 denoting the time when the first bit of the packet 204 is transmitted. When the packet 204 arrives at network device 202, a second timestamp 206 is taken to denote the time when the last bit of the packet 204 arrives at device 202. Then the addresses of the test packet 204 are modified and transmitted back to the device 201 containing the original timestamp 205, with the timestamp 206 and a timestamp 207 that denotes with the first bit of the packet 208 is transmitted on the network. When the final bit of the packet 208 arrives at the network device 201, a final timestamp 209 is taken. The difference in time between timestamp 205 and 206 ADDED to the difference in time between the timestamp 207 and 209 gives the total round-trip delay of the bi-directional path. Another method to determine the round-trip delay is to deduct the timestamp 205 from the timestamp 209. All intermediate nodes between the devices are not deemed relevant. It is also to be noted that the clocks between the network devices must be precisely synchronized by one of the many methods known to one skilled in the art.